Optimize wavelength to maximize contrast

Seasoned machine vision practitioners know that while the sensor and the optics are important, so too is lighting design. Unless an application is so “easy” that ambient light is enough, many or most value-added applications require supplemental light. “White” light is what comes to mind first, since it’s what we humans experience most. But narrow-band light – whether colored light within the visible spectrum, or non-visible light with a sensor attuned to those frequencies – is sometimes the key to maximizing contrast.

Gold contrasts better with red light than either white or blue – Image courtesy of CCS America

In the illustrations above, suppose we have an application to do feature identification for gold contacts. The ideal contrast to create is where gold features “pop” and everything that’s not gold fails to appear at all, or at most very faintly. If the targets that will come into the field of view have known properties, one can often do lighting design to achieve precisely such optimal outcomes

In this example, consider the white light image in the top left, and then the over-under images created with red and blue light respectively. The white light image shows “everything” but doesn’t really isolate the gold components. The red light does a great job showing just the gold (Au). The blue light emphasizes silver (Ag). The graph to the right shows four common metals relative to how they respond under which (visible) wavelengths. Good to know!

For an illustrated nine-page treatment of how various wavelengths improve contrast for specific materials or applications, download this Wavelength Guide from our Knowledge Base. You may be able to self-diagnose the wavelength ideal for your application. Or you may prefer to just call us at 978-474-0044, and we can guide you to a solution.

To the left we see 5 plastic contact lens packages, in white light. Presence/absence detection is inconclusive. Image courtesy of CCS America.

With UV light, a presence/absence quality control check can be programmed based on a rule that presence = 30% or more of the area in each round renders as black. Image courtesy of CCS America.

It all comes down to the reflection or absorption characteristics of specific properties with respect to certain wavelengths. Below we see a chart showing the peaks of some of the more commonly used wavelengths in machine vision.

Commonly used wavelengths – Image courtesy CCS America

For more details on enhancing contrast via lighting at specific wavelengths, download this Wavelength Guide from our Knowledge Base. Or click on Contact Us so we can discuss your application and guide you. 1stVision has several partners with different lighting geometries and wavelengths to create contrast. All three partners are in the same business group. CCS America and Effilux offer a variety of wavelengths (UV through NIR) and light formats (ring light, back light, bar light, dome). Gardasoft has full offerings for lighting controls. Tell us about your application and we’ll help you design an optimal solution.

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera and components selection.  With a large portfolio of lensescablesNIC card and industrial computers, we can provide a full vision solution!

EFFI Flex2 Lights – What’s New? 

EFFI-Flex2 LED bar lights

EFFI Flex2 LED bar lights are the next generation modular lights with even more flexibility. 

Series 1 vs. EFFI-Flex2 NextGen Series – courtesy of Effilux

Getting the lighting right is as important as choosing the right sensor, camera, and interface, in terms of machine vision success. Most all lights are “pre-configured” to a specific lighting geometry as well as wavelengths.  Lighting is still tricky and in most cases, testing is needed with various configurations. If your samples are small in size and don’t require special handling or equipment, your imaging partner may offer a lighting lab in which they can test your samples to optimize lighting configuration.

But shipping samples and re-creating your conditions in a partner’s lab isn’t always practical, and you may want to do your own testing and configuration, taking advantage of your domain expertise and home-field advantage. With EFFI Flex2 lights, the standard components and range of settings yield 36 configurations in 1 light! How so? Each unit comes with 3 diffuser windows x 4 lens positions x 3 electronic modes = 36 configurations. Optional additional accessories, like polarizers, take the calculation to more than 100 configurations!

EFFI Flex2 LED modular bar lights are configurable to a wide range of applications.  The user can adapt the optics, the electronics, and the mechanics, thanks to the engineering design.  Perhaps you’ll embed the unit in a “forever” deployment mode, never again re-configuring a specific unit once you lock down the optimal settings.

Or maybe you’ll adapt your light again to repurpose it in another application. With the long service life of LED lights, the light may well outlive the application. Or maybe you do multiple applications, and want a light that’s so versatile you can do all your testing in house, letting the lighting drive the final choice of sensor and camera model.

As with the first generation EFFI-Flex product, EFFI-Flex2 series is designed to provide easy adaptation of:

  • Optics – adjust the lens position and the diffusers
  • Electronics – built-in multimode driver offers 3 operating modes in one light
  • Mechanics – optical lengths from 60mm – 2900mm (factory configured)
One-minute video shows key optical and electronic configuration options

Optically,  lens positions may be user-adjusted for emission angles ranging from from 90 to 10 degrees. Each unit ships with swappable diffusers for strobed light, diffused, semi-diffused, or opaline light. Further, if necessary for your particular application, optional optical accessories are available: polarizer, linescan film, and cylindrical lens).

Electronically, the built-in multimode driver features 3 electronic modes: AutoStrobe with 450% Overdrive, Adjustable Strobe with controlled intensity from 10% to 100%, and Dimmable Continuous with controlled intensity from 10% to 100%. The 450% Overdrive mode is 1.5 times more powerful than the original EFFI-Flex LED bar light in overdrive.

The driver software makes it easy to select among the 3 modes, and the parameters within each mode.

Mechanics: While the length of a given unit cannot be adapted once delivered, one may order in lengths from as short at 60mm to as long as 2900mm. If your default units are English rather than metric, that’s from less than 3 inches to as much as 9.5 feet!

EFFI-Flex original series remains in production. If you don’t require the flexibility of EFFI-Flex2, with up to 36 configurations per unit shipped, the original series offers great value in its own right. Call us at 978-474-0044 to speak with one of our sales engineers, for guidance, or take out your own appendix with this side-by-side comparison diagram:

Series 1 vs. NextGen EFFI-Flex2 – courtesy of Effilux

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera and components selection.  With a large portfolio of lensescablesNIC card and industrial computers, we can provide a full vision solution!

Learn how an Allied Vision Mako camera can control your LED light source

camera as controller

In this article we discuss when and why one might want to strobe a light instead of using continuous lighting. While strobing traditionally required a dedicated controller, we go on to introduce that CCS and AVT have published an Application Note showing how the Allied Vision Mako camera can serve as the controller!

While LED lights are often used for continuous lighting, since that’s an easy mode of deployment, sometimes an application is best served with a well-timed strobe effect. This might be for one or more of the following reasons:

  • to “freeze motion” via light timing rather than shutter control alone;
  • to avoid the heat buildup from continuously-on lights
  • overwhelm ambient lighting
  • maximize lamp lifetime
Effilux LED lights

Let’s suppose you’ve already decided that you require strobe lighting in your application. You’re past “whether” and on to “how to”.

Since you are moving into the realm tight timing tolerances, it’s clear that the following are going to need to be coordinated and controlled:

  • the strobe light start and stop timing, possibly including any ramp-up delays to full intensity
  • the camera shutter or exposure timing, including any signal delays to start and stop
  • possibly the physical position of real world objects or actuators or sensors detecting these

Traditionally, one used and external controller, an additional device, to control both the camera and the lighting. It’s a dedicated device that can be programmed to manage the logical control signals and the appropriate power, in the sequence required. This remains a common approach today – buy the right controller and configure it all, tuning parameters through calculations and empirical testing.

Effilux pulse controller: controls up to 4 lights; output current can reach up to 1A @ 30V in continuous and 10A @ 200V in strobe mode – courtesy Effilux

Call us if you want help designing your application and choosing a controller matched to your camera and lighting requirements.

But wait! Sometimes, thanks to feature-rich lighting equipment and cameras, with the right set of input/output (I/O) connections, and corresponding firmware-supported functionality, one can achieve the necessary control – without a separate controller. That’s attractive if it can reduce the number of components one needs to purchase. Even better, it can reduce the number of manuals one has to read, the number of cables to connect, and the overall complexity of the application.

Let’s look at examples of “controller free” applications, or more accurately, cameras and lights that can effect the necessary controls – without a separate device.

Consider the following timing diagram, which shows the behavior of the Effi-Ring when used in auto-strobe mode. That doesn’t mean it strobes randomly at times of its own choosing! Rather it means that when triggered, it strobes at 300% of continuous intensity until the trigger pulse falls low again, OR 2 seconds elapse, whichever comes first. Then if steps down to continuous mode at 100% intensity. This “2 seconds max” feature, far longer than most strobed applications require, is a design feature to prevent overheating.

Courtesy Allied Vision Technologies

OK, cool. So where to obtain that nice square wave trigger pulse? Well, one could use a controller as discussed above. But in the illustration below, where’s the controller?!? All we see are the host computer, an Allied Vision Mako GigE Vision camera, an Effilux LED, a power supply, and some cabling.

Camera exposure signal controls strobe light – courtesy Allied Vision Technologies

How is this achieved without a controller? In this example, the AVT Mako camera and the Effilux light are “smart enough” to create the necessary control. While neither device is “smart” in the sense of so-called smart cameras that eliminate the host computer for certain imaging tasks, the Mako is equipped with opto-isolated general purpose input output (GPIO) connections. These GPIOs are programmable along with many other camera features such as shutter (exposure), gain, binning, and so forth. By knowing the desired relationship between start of exposure, start of lighting, and end of exposure, and the status signals generated for such events, one can configure the camera to provide the trigger pulse to the light, so that both are in perfect synchronization.

Note: During application implementation, it can be helpful to use an oscilloscope to monitor and tune the timing and duration of the triggers and status signals.

Whether your particular application is best served with a controller, or with a camera that doubles as a controller, depends on the application and camera options available. 1stVision carries a wide range of Effilux LED lights in bar, ring, backlight, and dome configurations, together with the ability to be used on continuous or strobe modes.

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera and components selection.  With a large portfolio of lensescablesNIC card and industrial computers, we can provide a full vision solution!

Machine vision lights as important as sensors and optics

Lighting matters as much or more than camera (sensor) selection and optics (lensing). A sensor and lens that are “good enough”, when used with good lighting, are often all one needs. Conversely, a superior sensor and lens, with poor lighting, can underperform. Read further for clear examples why machine vision lights are as important as sensors and optics!

Assorted white and color LED lights – courtesy of Advanced Illumination

Why is lighting so important? Contrast is essential for human vision and machine vision alike. Nighttime hiking isn’t very popular – for a reason – it’s not safe and it’s no fun if one can’t see rocks, roots, or vistas. In machine vision, for the software to interpret the image, one first has to obtain a good image. And a good image is one with maximum contrast – such that photons corresponding to real-world coordinates are saturated, not-saturated, or “in between”, with the best spread of intensity achievable.

Only with contrast can one detect edges, identify features, and effectively interpret an image. Choosing a camera with a good sensor is important. So is an appropriately matched lens. But just as important is good lighting, well-aligned – to set up your application for success.

What’s the best light source? Unless you can count on the sun or ambient lighting, or have no other option, one may choose from various potential types of light:

  • Fluorescent
  • Quartz Halogen – Fiber Optics
  • LED – Light Emitting Diode
  • Metal Halide (Mercury)
  • Xenon (Strobe)
Courtesy of Advanced Illumination

By far the most popular light source is LED, as it is affordable, available in diverse wavelengths and shapes (bar lights, ring lights, etc.), stable, long-life, and checks most of the key boxes.

The other light types each have their place, but those places are more specialized. For comprehensive treatment of the topics summarized here, see “A Practical Guide to Machine Vision Lighting” in our Knowledgebase, courtesy of Advanced Illumination.

Download whitepaper
Download whitepaper

Lighting geometry and techniques: There’s a tendency among newcomers to machine vision lighting to underestimate lighting design for an application. Buying an LED and lighting up the target may fill up sensor pixel wells, but not all images are equally useful. Consider images (b) and (c) below – the bar code in (c) shows high contrast between the black bars and the white field. Image (b) is somewhere between unusable or marginally usable, with reflection obscuring portions of the target, and portions of the (should be) white field appearing more grey than white.

Courtesy of Advanced Illumination

As shown in diagram (a) of Figure 22 above, understanding bright field vs dark field concepts, as well as the specular qualities of the surface being imaged, can lead to radically different outcomes. A little bit of lighting theory – together with some experimentation and tuning, is well worth the effort.

Now for a more complex example – below we could characterize images (a), (b), (c) and (d) as poor, marginal, good, and superior, respectively. Component cost is invariant, but the outcomes are sure different!

Courtesy of Advanced Illumination

To learn more, download the whitepaper or call us at (978) 474-0044.

Contact us

Color light – above we showed monochrome examples – black and white… and grey levels in between. Many machine vision applications are in fact best addressed in the monochrome space, with no benefit from using color. But understanding what surfaces will reflect or absorb certain wavelengths is crucial to optimizing outcomes – regardless of whether working in monochrome, color, infrared (IR), or ultraviolet (UV).

Beating the same drum throughout, it’s about maximizing contrast. Consider the color wheel shown below. The most contrast is generated by taking advantage of opposing colors on the wheel. For example, green light best suppresses red reflection.

Courtesy of Advanced Illumination

On can use actual color light sources, or white light together with well-chosen wavelength “pass” or “block” filters. This is nicely illustrated in Fig. 36 below. Take a moment to correlate the configurations used for each of images (a) – (f), relative to the color wheel above. Depending on one’s application goals, sometimes there are several possible combinations of sensor, lighting, and filters to achieve the desired result.

Courtesy of Advanced Illumination

Filters – can help. Consider images (a) and (b) in Fig. 63 below. The same plastic 6-pack holder shown is shown in both images, but only the image in figure (b) reveals stress fields that, were the product to be shipped, might cause dropped product, reduced consumer confidence in one’s brand. By designing in polarizing filters, this can be the basis for a value-added application, automating quality control in a way that might not have been otherwise achievable – or not at such a low cost.

Courtesy of Advanced Illumination

For more comprehensive treatment of filter applications, see either or both Knowledgebase documents:

Powering the lights – should the be voltage-driven or current-driven? How are LEDs powered? When to strobe vs running in continuous modes? How to integrate light controller with the camera and software. These are all worth understanding – or having someone in your team – whether in-house or a trusted partner – who does.

For comprehensive treatment of the topics summarized here, see Advanced Illumination’s “A Practical Guide to Machine Vision Lighting” in our Knowledgebase:

Download whitepaper
Download whitepaper

This blog is intended to whet the appetite for interest in lighting – but it only skims the surface. Machine vision lights as important as sensors and optics. Please download the guide linked just above – to deepen your knowledge. Or if you want help with a specific application, you may draw on the experience of our sales engineers and trusted partners.

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera and components selection.  With a large portfolio of lensescablesNIC card and industrial computers, we can provide a full vision solution!